The present invention relates to new and improved epoxy resin compositions. More particularly, it relates to curable epoxy resin compositions comprising reinforcing filaments and epoxy resin(s) combined with certain aromatic ether-sulfone polyamine curing agents.
Epoxy resin compositions are useful to encapsulate electronic components, and as structural adhesives, and the like. Reinforced epoxy resin composites having high strength to weight ratios have found extensive use in the aircraft and aerospace industries, and in other applications where strength, corrosion resistance and light weight are desirable. For instance, fiber resin matrix materials have replaced aluminum and other metals in primary and secondary structures of modern military and commercial aircraft. Sporting equipment such as tennis rackets and golf clubs have also adopted fiber resin materials successfully.
Epoxy resin compositions and fiber modifications are abundant. Since the advent of fiber resin matrix materials, much effort has been expended in improving their properties and characteristics, including the development of many different curing systems.
Amine and polyamine curing agents have received wide acceptance, but the toxicity, low solubility, high exotherm and variable curing rates associated with the most commonly used amines, such as m-phenylenediamine, 4,4'-diaminodiphenyl methane and 4,4'-diaminodiphenyl sulfone, has made further improvement desirable. In the case of aircraft structural applications, epoxy resins cured with available curing agents are either too brittle or do not have sufficient strength and stiffness under hot/wet conditions. It is disclosed in U.K. Pat. No. 1,182,377, which is incorporated herein by reference, that certain aromatic polyamines having the formula: ##STR1## wherein R represents the radical formed after elimination of the hydroxyl group of a polyhydric aliphatic, cycloaliphatic or araliphatic alcohol, Ar represents an optionally substituted phenylene or naphthylene radical, R' represents hydrogen or an alkyl radical and n represents an integer from 2 to 10, are effective as curing agents for a variety of polyepoxides, and the resulting cured compositions are useful as films, moldings, coatings and glass-reinforced laminates. There is no indication in the properties presented in the U.K. Patent that the curing agents exemplified therein will produce the combination of toughness and strength under hot/wet conditions essential for use in the above-mentioned structural applications.
In U.S. Pat. No. 3,932,360, diamine cured polyurethane products are described, in which the diamines are of the formula, e.g., ##STR2## wherein n is an integer from 2 to 12. This U.S. Pat. No. 3,932,360 does not deal with curing compounds having more than one epoxide group per molecule.
In Gillhan et al, Organic Coatings and Applied Polymer Science Proceedings, Vol. 46, p. 592-598, March-April, 1982, polyepoxides cured with diamines of the immediately preceding formula (n is 3), are described.
In Chemical Abstracts, 90:39660y, bis(aminophenoxy) compounds, such as 4,4'-bis(3-aminophenoxy)diphenylsulfone, are disclosed to be useful crosslinking agents for bisphenol-A-epichlorohydrin copolymer resins and provide improved heat distortion temperature and improved flexibility to that cured epoxy resin, as compared with a similar composition cured with a diaminophenylmethane crosslinking agent.
In Chemical Abstracts, 91:158766t thermosetting resin laminates having good flexibility and machinability are disclosed which are, prepared by impregnating a glass textile with a thermocurable composition comprising an epoxy resin (ARALIDITE.RTM.8011, from Ciba-Geigy Corporation); a diamine of the formula: ##STR3## where Z.sup.1, Z.sup.2 and Z.sup.3 are O, S, SO.sub.2, CH.sub.2, CO, CO.sub.2 or C(CH.sub.3).sub.2 and 2-ethyl-4-methylimidazole; processing the impregnated fabric at 160.degree. C. to form a prepreg; laying up several layers of prepregs and fusing at 170.degree. C. and 90 Kg/cm.sup.2 for 11/2 hours.
It has now been discovered that new and improved curable epoxy resin compositions and fiber-resin matrix compositions are provided in the form of epoxy resin compositions comprising an epoxy resin(s) and a curing agent selected from certain aromatic ether-sulfone polyamine compounds. The present invention provides neat resn formulations which after curing exhibit improved flexural failure strength and strain, and improved hot/wet modulus. When the epoxy compositions of the present invention are cured with non-siliceous filaments to form reinforced composites, the composites exhibit improved interlaminar toughness, compression strength, and short beam shear strength under dry, wet or hot/wet conditions.
In the epoxy art, the term "epoxy resin" refers to a compound having more than one epoxy group per molecule, capable of being cured to a polymeric state.